What are the guidelines for using Piriton (chlorpheniramine) for allergic reactions?

Piriton (Chlorpheniramine) for Allergic Reactions

Piriton (chlorpheniramine) is an adjunctive medication only and should never be used as first-line treatment for allergic reactions—epinephrine is the only appropriate first-line therapy for anaphylaxis, and delaying epinephrine administration to give antihistamines significantly increases risk of death. 1

Critical Safety Warning

• Using antihistamines instead of epinephrine is the most common reason for failure to administer epinephrine and places patients at significantly increased risk for life-threatening progression 1
• Delayed epinephrine administration is repeatedly implicated in anaphylaxis fatalities 1
• Chlorpheniramine itself can paradoxically cause anaphylaxis, though rare—17 of 54 reported adverse reactions (31.5%) were anaphylactic in one pharmacovigilance database 2

When Chlorpheniramine May Be Used

For Mild Allergic Reactions (NOT Anaphylaxis)

• Chlorpheniramine can be used for isolated mild symptoms: flushing, urticaria, mild angioedema, or oral allergy syndrome 1
• However, continuous monitoring is mandatory to detect progression to anaphylaxis 1
• If any progression occurs, immediately administer epinephrine—do not give additional antihistamines 1

As Adjunctive Therapy After Epinephrine

• Chlorpheniramine may be given only after adequate resuscitation with epinephrine and fluids 1
• In perioperative anaphylaxis, chlorpheniramine showed no evidence of harm but also no proven benefit 1
• Dosing after anaphylaxis treatment: Diphenhydramine (similar first-generation antihistamine) 1-2 mg/kg every 6 hours for 2-3 days, maximum 50 mg per dose 1
• Chlorpheniramine is not prioritized in current guidelines—diphenhydramine is more commonly recommended 1

Treatment Algorithm for Allergic Reactions

Step 1: Assess Severity

• Anaphylaxis criteria: Acute onset with skin/mucosal involvement PLUS respiratory compromise OR hypotension OR two organ systems involved after allergen exposure 1
• Mild reaction: Isolated urticaria, flushing, or mild angioedema without systemic symptoms 1

Step 2: Immediate Management Based on Severity

For Anaphylaxis:

1. Epinephrine IM immediately (anterolateral thigh): 0.01 mg/kg of 1:1,000 solution, maximum 0.3 mg in children <25 kg, 0.5 mg in adults 1
2. Repeat epinephrine every 5-15 minutes if inadequate response 1
3. Place patient supine with legs elevated 1
4. Administer IV fluids for hypotension 1
5. Supplemental oxygen 1
6. Only after stabilization: Consider chlorpheniramine or diphenhydramine 1

For Mild Reactions:

1. H1 antihistamine (chlorpheniramine or diphenhydramine) 1
2. Monitor continuously for 4-6 hours for progression 1
3. Have epinephrine immediately available 1
4. If history of prior severe reaction, give epinephrine at first sign of symptoms—do not wait 1

Step 3: Discharge Management

• Continue antihistamine for 2-3 days: Diphenhydramine every 6 hours or non-sedating second-generation antihistamine 1
• Add H2 antihistamine (ranitidine) twice daily for 2-3 days 1
• Corticosteroid (prednisone) daily for 2-3 days 1
• Prescribe epinephrine auto-injector (two doses) with training 1

Specific Clinical Contexts

Urticaria Management

• Second-generation non-sedating antihistamines are first-line for chronic urticaria, not chlorpheniramine 3
• Chlorpheniramine (first-generation) causes sedation and anticholinergic effects 4
• If first-generation antihistamine needed, use at nighttime only for pruritus control 4, 5

Special Populations Requiring Caution

• Pregnancy: Chlorpheniramine is often preferred over hydroxyzine if antihistamine needed, but avoid in early pregnancy 4
• Renal impairment: Halve dose in moderate impairment; avoid in severe impairment 4
• Liver disease: Avoid in severe hepatic disease due to sedation 4, 5
• Elderly: Avoid due to anticholinergic effects and cognitive impairment risk 5

Common Pitfalls to Avoid

1. Never substitute chlorpheniramine for epinephrine in anaphylaxis—this is the leading cause of preventable anaphylaxis deaths 1
2. Do not give chlorpheniramine IV during active anaphylaxis as priority treatment—it provides no benefit for life-threatening symptoms 1
3. Do not assume chlorpheniramine is completely safe—it can cause hypersensitivity reactions including anaphylaxis, particularly in aspirin-intolerant patients 2, 6
4. Do not use chlorpheniramine as monotherapy for asthma or bronchospasm—bronchodilators (albuterol) are required 1
5. Do not discharge patients after mild reactions without observation period—biphasic reactions can occur; observe minimum 4-6 hours 1